The invention relates generally to locomotive propulsion systems and, in particular, to locomotive controllers for selectively limiting tractive effort in locomotives.
Compared to earlier locomotives, such as locomotives equipped with a DC (direct current) propulsion system, locomotives equipped with an AC (alternating current) propulsion system generally produce at low speeds substantially more tractive effort and provide higher adhesion to the rails. When the locomotive is used for heavy hauling application, such as the hauling of bulk materials, grain, etc., this high tractive effort is desirable. However, the high tractive effort provided by these high performance locomotives, as may be part of a remote consist of locomotives in a relatively light hauling application, could cause lifting or derailment of one or more cars under certain conditions, particularly in curvy terrain. Examples of factors that may adversely affect operation of the train may include the presence of one or more lighter cars, uneven tonnage distribution, the presence of one or more empty cars in the train, etc.
In view of the foregoing considerations, it would be desirable to provide system and techniques that would enable a controllable reduction in locomotive tractive effort. This would avoid operation in modes of high tractive effort to reduce the tendency of some of the railcars to lift from the rail tracks and hence avoid the possibility of derailment, such as could occur in the event the high tractive effort is not commensurate with the actual characteristics of the train load, such as magnitude of the load, uneven distribution of the load, etc. Thus, this invention in one aspect thereof, selectably reduces the maximum tractive effort generated by locomotives used in remote distributed power applications, while retaining their full horsepower at higher speeds where tractive effort is typically reduced. It would be further desirable to allow users of locomotive fleets to be able to quickly and reliably configure a locomotive capable of delivering high tractive effort for multiple applications, such as those where high tractive effort is required as well as for applications that otherwise would call for lower rated locomotives.